Colloidal quantum dots (QDs) are superior to organic luminescent materials for display and lighting applications due to their narrow emission bandwidths, high photoluminescence quantum efficiency and tenability of their emission spectrum through particle size control. However, despite year of intense research, quantum dot light-emitting diode (QLED) devices that utilize electroluminescence properties of QDs have remained inferior to organic light-emitting diode (OLED) devices in terms of brightness, efficiency, and operational lifetime prior to this invention.
Photomedical applications include photodynamic therapy (PDT) and photobiomodulation (PBM). In PDT, light of specific wavelengths is used to excite photosensitizers (i.e., drugs that are nontoxic themselves, but can be activated by light exposure) and to turn molecular oxygen into singlet oxygen that can kill unwanted tissues, cells (including cancer cells, bacteria, fungi and viruses) and thus lead to the treatment of cancers, infections, etc. In PBM, light can enhance cellular function, leading to beneficial clinical effects, such as wound repair or hair regrowth.
PDT and PBM have been clinically demonstrated as effective, minimally invasive or noninvasive strategies for treating cancer and other infections, for improving wound repair, for reducing pain and for hair regrowth. However, they have not received widespread acceptance mainly because of the challenging light source requirements, wherein the ideal light source needs to emit the appropriate color within a narrow emission spectrum to match the absorption peaks of the photosensitizers, needs to exhibit a high enough power density for sufficient excitation but also produce low enough heat to avoid pain for the patients in addition to providing flexible form factors with homogeneous emission so that the light source can be easily applied to the patients without worrying about over or under treatments.
Currently, laser and light-emitting diodes (LEDs) are the dominant light sources used in the field of photomedicine because they can provide adequate power density at the proper wavelength window. However, these expensive, hot, rigid, heavy and inhomogeneous light sources are not commonly available in small clinics and treatments can only be carried out in limited places and require expensive hospital visits, thereby limiting their further penetration into practical clinical use.
Organic light-emitting diodes (OLEDs) have previously been proposed for use in photomedicine. However, existing OLEDs are unable to achieve the required high light brightness (>20,000 cd/m2 or ˜10 mW/cm2) at wavelengths within the deep red region due to the significant efficiency roll-off problems of OLEDs at high current density and the lack of efficient deep red emitters having narrow spectra.
Accordingly, what is needed in the art is a quantum dot light-emitting (QLED) device having improved efficiency and exhibiting high driving conditions capable of achieving brightness level>100,000 cd/m2. Such improved QLED devices can be applied in the field of photomedicine.